How is it that Western music can satisfy harmonic and contrapuntal constraints at
once? What determines whether two chords can be connected by efficient voice leading?
Musicians have been investigating these questions for almost three centuries. The circle of
fifths (Fig. S1), first published in 1728 (4), depicts efficient voice leadings among the
twelve major scales. The Tonnetz (Fig. S2), originating with Euler in 1739, represents
efficient voice leadings among the twenty-four major and minor triads (2, 5). Recent work
(5–13) investigates efficient voice leading in a variety of special cases. Despite tantalizing
hints (6–10), however, no theory has articulated general principles explaining when and
why efficient voice leading is possible. This report provides such a theory, describing
geometrical spaces in which points represent chords and line segments represent voice .